\documentclass{article}
\usepackage{pstricks}
\usepackage[icelandic,USenglish]{babel}
\usepackage[T1]{fontenc}
\parindent0pt
\begin{document}
  My coauthor is 
  \foreignlanguage{icelandic}{{\dh}r{\'u} {\TH}horsten}
  
  \begin{abstract}
    Our paper deals with \ldots
  \end{abstract}

  If you want the abstract also in Icelandic, write
  \selectlanguage{icelandic}
  \begin{abstract}
    {\dh}r{\'u} {\TH}horsten \ldots
  \end{abstract}
  
  \selectlanguage{USenglish}
  Don't forget to switch back to English.
  
  \begin{table}[h]
  \caption{A table}
  \end{table}
  
  You could also add another table in Icelandic (although this doesn't make sense):
  \selectlanguage{icelandic}
  \begin{table}[h]
  \caption{An Icelandic table by {\dh}r{\'u} {\TH}horsten}
  \end{table}
  
\end{document}